Shadow mask supported by v-shaped springs having apices directed toward gun



Jan. 27, 197.0 P- PAPPADIS l3,492,522

SHADOW VIVASK SUPPORTED BY V-SHAPED SPRINGS HAVING APIcEs DIRECTED TOWARD GUN Filed Aug. 15, 19e? mi 2| 22 n Invenror Nicholas P. Poppcdis United States Patent U.S. Cl. 313-85 4 Claims ABSTRACT OF THE DISCLOSURE A shadow mask assembly for a color cathode-ray tube has the aperture mask supported on an open frame which is provided with resilient mounting springs, individually anchored at one end to the frame and having a hole at the free end for receiving mounting studs provided within the envelope of the tube to position the mask assembly in essentially spaced parallel relation to the faceplate. The mounting springs extend generally vertically but are tilted at an acute angle away from the plane of the mask and in the direction of the gun mount to displace the assembly toward the faceplate as the mask assembly heats up in the operation of the tube. For a typical 25 inch tube, the angle of inclination of the mounting springs is approximately 25.

In another embodiment, each of the mounting springs is V-shaped having one leg xed to the frame of the mask assembly and having the other apertured to receive the mounting stud of the tube envelope. The angle defined by these legs is preferably about 45. The position of the V-shaped spring is such that it faces the aperture mask.

BACKGROUND OF THE INVENTION The shadow mask of the tube type under consideration is the means by which color selection is attained. The mask has a pattern of apertures disposed in a field which corresponds to the configuration of the image screen of the tube and is positioned between the screen and the gun mount, typically comprising three electron guns for producing three beams of electrons. The arrangement is such that the electron beam issuing from any such gun, in reaching the screen of the tube through the apertures of the shadow mask, is permitted to impinge only upon those screen elements which emit light of the particular color to which that gun has been assigned. For example, where the screen is comprised of an interlaced multiplicity of dot triads of blue, green and red emitting phosphors, one gun sees only green phosphor dots; a second is permitted to see only blue phosphor dots and the remaining one sees nothing but red phosphor dots. In performing this function of color selection, the shadow mask intercepts a significant portion of each electron beam and in the operation of the tube dissipates a considerable quantity of heat. It is not uncommon for a mask to attain a temperature of 80 C.

The temperature rise experienced as the mask assembly attains its operating temperature can be expected to be accompanied by expansion of the mask components which causes the apertures of the mask to be displaced transversely of the beam paths resulting in rnisregistration of the beams with the phosphor dots. This is evident when it is recalled that the phosphor dots are generally deposited on the image screen through a photographic technique in which the mask of the tube is utilized in locating the series of dots constituting the phosphor pattern. Any subsequent distortion of the aperture pattern results in misregistration or error in the beam 3,492,522 Patented Jan. 27, 1970 ICC landings relative to the phosphor dots over the image raster. Of course, the temperature rise of the mask assembly cannot be avoided and, therefore, it is necessary to take steps to minimize misregistration. In general, this requires arranging to have movement of the assembly, attributable to expansion, restricted to movement along the intended paths of the beams.

Actually, the assembly comprises a heavy frame to which a large-area, light-weight apertured mask is afiixed. At the start of operation, the mask temperature rises quickly because it is a large area bombarded by electrons and because it is a much smaller mass than the frame. Consequently the mask expands first but, if it is constructed in accordance with the teachings of Patent 2,897,- 392 issued July 28, 1959 in the name of Joseph P. Fiore, this merely causes doming or displacement of the apertures essentially along the intended beam paths with a minimal amount of misregistration. The frame, on the other hand, requires two to three hours of operation to reach equilibrium temperature and continues to expand long after the mask has stabilized. Expansion of the frame tends to flatten the mask and displaces the apertures thereof transversely. Unless compensated in some fashion, the expansion of the frame introduces unwanted misregistration.

A method of fabricating the mask assembly is described and claimed in an application Ser. No. 443,467, filed Mar. 29, 1965, in the name of Joseph P. Fiore and likewise assigned to the assignee of the present invention. This method is also directed to minimizing the adverse effects of high temperatures with reference to the precision of beam landings. The present invention is a further improvement in the structure of the mask assembly for minimizing misregistration.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a shadow mask assembly for a color cathode-ray tube which is further improved in the matter of maintaining proper registration of the electron beams with the elemental areas of the image screen in spite of the temperature rise of that assembly in the operation of the tube.

It is a speciiic object of the invention to arrange the mask assembly to the end that movement of the assembly attributable to temperature rise is in the direction of the image screen.

It is a specific object of the invention to improve the shadow mask assembly to minimize changes of the beam paths through the shadow mask to the image screen as the tube achieves operating temperature.

The shadow mask assembly of the invention is for use in a color cathode-ray tube having an envelope with a faceplate at one one bearing a pattern of phosphor deposits and with mounting studs disposed on internal Walls in the immediate vicinity of the faceplate. Such a tube also has a gun mount at the opposite end of the envelope for directing at least one but usually three electron beams along given paths to the phosphor pattern. The improved shadow mask assembly comprises a metallic open frame having essentially the same configuration as the phosphor pattern and a metallic aperture mask having a mounting flange which is mechanically secured to the frame and which encloses a pattern of apertures corresponding to the phosphor pattern. Where the phosphor pattern is the well known dot triad, the mask is provided with circular holes, one for each triad. For a screen having strips of phosphor, the mask takes the form of a grid of parallel arranged conductive wires. A pair of similar metallic and resilient mounting springs are fixed at one end to opposite side portions of the frame and extend away from the plane of the mask in the direction of the gun mount at a predetermined angle. The free end of each spring has provisions, usually mounting holes, for engaging the mounting studs of the tube envelope to position the mask assembly in substantially spaced parallel relation to the faceplate. The angular relation of the mounting springs to the mask frame effects displacement of the assembly in the direc tion of the faceplate as the mask assembly, when mounted within the operating tube, achieves its operating temperature.

BRIEF DESCRIPTION OF THE DRAWING The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in the several figures of which like reference numerals identify like elements, and in which:

FIGURE 1 is a schematic representation of a color cathode-ray tube having a shadow mask assembly embodying the invention;

FIGURE 2 is a sectional view showing more clearly the installation of the mask assembly within the tubeenvelope;

FIGURE 3 is a fragmentary view taken along lines 3 3 of FIGURE 1;

FIGURE 4 is a fragmentary view of the central top portion of the mask assembly; and

FIGURE 5 shows a view, taken in the same plane as FIGURE 3, of a modified form of mounting spring aro rangement for the mask assembly.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now more particularly to FIGURE 1, the color cathode-ray tube there represented has an envelope terminating at one end in a cap or faceplate 11 which serves as the screen or image area of the tube. The internal surface of faceplate 11 bears a phosphor pattern 12 which may take any of a variety of different arrangements. Usually, the pattern is an interlaced arrangement of phosphor strips or phophor dots arranged in the form of triads. The latter is the more conventional and it will be assumed that pattern 12 is of that type. In such a case, the three elements of any triad are deposits of red, blue and green emitting phosphors. The screen and phosphor pattern is backed by a conductive and light reflecting layer 13 of aluminum.

A tube of the type under consideration has a parallax element '20 supported in spaced parallel relation with respect to its screen 12 by means of mounting studs 14 formed integrally on the internal side walls of the envelope in the immediate vicinity of the faceplate and a similar mounting stud 15 located in the center portion of the upper internal wall of the envelope.

At the opposite or neck end of envelope 10, there is supported the customary gun mount 16 for directing at least one electron beam along a given path to screen 12. Usually, this mount is a cluster of three guns each of which issues an electron beam which, in traversing the shadow mask assembly 20 presently to be described, impinges on only an assigned member of each of the triads of screen 12 as these beams are caused to scan over the image area of the tube. As indicated above, one such beam impinges on the red emitting phosphor elements only and the remaining two impinge on the green and blue emitting phosphor elements, respectively.

If the structural details of mask assembly 20 be ignored for the moment, the described arrangement is a typical or conventional dot type shadow mask color tube. Both its structure and method of operation are well understood in the art and, therefore, need be alluded to only in cursory fashion.

When the cathodes of gun mount 16 have attained operating temperature, they issue electrons which are formed into three electron beams that are accelerated through mask assembly 20 to screen 12. Per force of the geometry of the gun mount and the aperture mask of assembly 20, each beam impinges upon or sees only its assigned elemental phosphor dots. Deflection fields established through the appropriate energizaton of a deflection yoke (not shown) cause the three beams to scan the screen 12 at the same time those beams are appropriately modulated with luminance and chrominance information. In this way, an image in simulated natural color is synthesized on the screen. Of course, necessary accessories such as dynamic convergence are associated with a tube of this type but they constitute no part of the present invention and have not been shown nor will they be described further.

More particular consideration will now be given to mask assembly 20 constructed in accordance with the invention so that the paths of the beams suffer no material dislocation or interruption as that assembly is brought to operating temperature under the influence of the scanning electron beams. As stated above, electrons impinge on this assembly in the operation of the tube causing the dissipation of a significant amount of heat with consequent expansion of the component parts but where they are arranged as taught herein, such displacement or movement of the parts as may be encountered has a minimal adverse effect on the beam-dot landings or registration.

The mask assembly is basically the same as that dcscribed in FiOre Patent 2,897,392 comprising a metallic open frame 21 having esentially the same configuration as the phosphor pattern of screen 12. That is to say, where the tube has an image area of rectangular configuration, frame 20 has a similar configuration. It is formed of relatively heavy stock, such as 93 mil cold rolled steel so that in comparison with its associated aperture mask 22, the frame is a massive structure. The frame material is essentially L-shaped in cross section having a part 2lb that is parallel to the plane of mask 22 and a part 21a that is normal to the plane of the mask.

Mask 22 is also .metallic and may for example be formed of very thin sheet steel of approximately 6 mil stock. It has an imperforate skirt or mounting flange 22a which is formed to telescope over portion 21a of frame 21 and is mechanically secured thereto to integrate these components together. Flange 22a encloses a pattern 221) of apertures corresponding to the phosphor pattern of screen 12. For the screen arrangement assumed to have been deposited on surface 12, the apertures are circular and are disposed in a rectangular field with one aperture aligned with each dot triad of screen 12 in known fashion.

Mask assembly 20 is secured within envelope 10 in substantially spaced parallel relation to faceplate 11 by .means of resilient mounting springs that engage mounting studs 14 and 1S. While a four point suspension of the mask assembly is used in some tube structures, a three point arrangement has been illustrated in FIGURE 2. It has mounting springs on opposing side portions of frame 21 and a mounting spring centrally located at the top of the frame. The side mounts are two metallic and similar resilient springs 23 fixed at one end 23a to the opposite side portions of the frame and extending away from the plane of mask 22 at a predetermined angle 0 as shown in FIGURE 1. For the side suspension, springs 23 are secured below the center line of frame 21 approximately two-thirds the way down from the upper surface thereof. They extend vertically upwardly at an acute angel 0 with the plane of mask 22. The free ends of springs 23 have provisions for engaging mounting studs 14. These provisions take the form of generally triangular shaped holes 23b dimensioned to receive mounting studs 14.

As revealed in FIGURE 2, these springs have a flat portion 23a for welding to frame 21, a canted section and another essentially flat portion 23e which accommodates mounting hole 23b. The angular relation of portion 23C to the slant part of the spring is preferably chosen So that portion 23C is normal to the axis of mounting stud 14. The angular relation of springs 23 with respect to frame 21 causes expansion of the mask assembly as that assembly achieves operating temperature in the operation f the tube, to be converted into displacement of the assembly, in the direction of faceplate 11.

This is most readily understood from a consideration of FIGURE 3, showing the projection of one mounting spring 23 in X-Y plane, that is, a plane transverse to the plane of mask 22. The dimension x is the spacing between frame 21 and stud 14 in the reference condition in which the mask is at ambient temperature. This spacing is in accordance with the following:

x==1 sin w y=1 cos 1:1 sin 0 (2) and tan w==sin w y sin 0 (3) From these relations it is established that transverse movement of the mask assembly which leads to misregistration is converted to .movement in the direction of screen 12 as required to minimize misregistration.

More particularly, transverse expansion of the frame decreases spacing x and compresses spring 23 but one end of the spring is fixed at stud 14 and the other is fixed at frame 21. The force has a component in the y direction which moves the assembly toward screen 12. If angle w is 45 in the reference condition, the movement in the direction of the screen is approximately equal to the change in spacing x and misregistration is minimized.

One embodiment of the invention in a 25 inch shadow mask tube, found to minimize misregistration as assembly 20 achieves operating temperature, was in accordance with the following:

Mask 21: `6 mils, cold rolled steel having a coefficient of expansion :of 13X106 in./in./ C.

Springs 23: 32 mils, stainless steel having a coefficient of expansion of 16 106 in./in./ C.

Angle 0: Approximately 25.

Angle w: Approximately 45.

Hole 23h to closest spring weld: Approximately 11/2 inch.

The arrangement constructed with the illustrative paramete'rs recited above exhibited minimal change in the paths :of the electron beams even as frame 21 achieved its operating temperature.

lOf course, there are means on the assembly for engaging mounting stud 15 to complete the three point suspension. As indicated in FIGURE 4, this means is another spring having two sections 25, 25a. One end of each is welded to the central top portion of frame 21 and they are canted to define a V-facing mask 22. The mounting hole 25b is at the apex of the V to receive mounting stud 15. In the illustrative structure disclosed above, the angle of spring sections 25, 25a with a plane transverse to the longitudinal tube axis was appproximately 45 In conguration, the spring sections 25, 25m are very similar to that of the first described springs 23.

FIGURE is a modified arrangement, featuring mounting springs that are generally V-shaped with the apex positioned away from the mask. As stated above, frame 21 is L-shaped in cross section having one part 2lb that is parallel and another part 21a that is normal to the plane of mask 22. One leg 30 of the V-shaped spring is welded to frame part 2lb and the other leg portion 30a is disposed essentially parallel to frame part 21a and parallel to the longitudinal axis of the tube. The free end of leg 30a has an aperture 30b for receiving mounting stud 14. The angle defined by legs 30, 30a of the spring is preferably approximately 45.

Where this form of mounting spring is adopted, it may be conveniently employed at each of the three suspension points. Any expansion of the mask assembly results in a force component directed toward the mask and if the angle of the spring is 45 as stated, the force components in the direction of the mask and in a direction parallel to the mask are substantially equal. This causes any movement of the assembly experienced with heating up to be essentially along the desired beam path and minimizes problems of misregistration.

It is entirely feasible and preferred to have spring leg 30 of a softer or more resilient stock than leg 30a. The stiffer element 30a is desired for properly positioning the mask assembly within the tube envelope and the softer element 30 provides the desired conversion of expansion forces into at least one component directed toward the screen. Moreover, since the V-shaped springs 30, 30a have apices remotely located relative to mask 22, they are easily grasped and maneuvered to simplify inserting the mask assembly 20 into the tube envelope. Of course, the envelope is made of two parts, a cap section containing faceplate 11 with a fiange accommodating mounting studs 14, 15 and a second portion containing most of the conical section of the envelope plus the neck. Mask insertions and manipulations are made While these parts of the envelope are separated and, after the screen has been formed and the mask assembly finally installed, the envelope sections are integrated as well understood.

In one embodiment of the arrangement of FIGURE 5 for a 25" rectangular tube, spring 30 was stainless steel with a thickness of 0.023l and a length of 1.000. Spring 30a was of the same material but had a thickness of 0.042" and a length of 1.125.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. A shadow mask assembly for a color cathode-ray tube having an envelope with a `faceplate at one end bearing an interlaced pattern of deposits of different phosphor materials and with mounting studs disposed on internal walls in the immediate vicinity of said faceplate and further having a gun mount at the opposite end of said envelope for directing at least one electron beam along a given path to said phosphor pattern, said assembly comprising:

a metallic open frame having essentially the same configuration as said phosphor pattern;

a metallic aperture mask having a mounting flange mechanically secured to said frame and enclosing a pattern of apertures corresponding to said phosphor pattern; and pair of similar metallic, resi1ient mounting springs fixed to opposite side portions of said frame and individually of substantially V-shaped configuration with its apex positioned away from said mask in the direction of said gun mount, having only one leg portion affixed to said frame and having in the free end of the other leg portion thereof provisions for engaging one of said mounting studs to support said assembly in substantially spaced parallel relation to said faceplate, said side portions of said frame being I.shaped in cross section and having one part parallel and another part normal to the plane of said mask, said one leg portion of each V-shaped spring being aixed to said parallel part of said frame.

2. A shadow mask assembly in accordance with claim 1 in which said other leg portion of said V-shaped spring is substantially parallel to said other part of said frame.

7 3. A shadow mask assembly in accordance with claim 1 in which the angle defined by said leg portions of said spring is approximately 45.

4. A shadow mask assembly in accordance with claim 1 in which the material of said one leg portion of said V-shaped spring is more resilient than the material of said other leg portion thereof.

References Cited UNITED STATES PATENTS 8 Shrader.

ROBERT SEGAL, Primary Examiner U.S. Cl. X.R. 

